Prepare a scene (preview)

Prepare a scene: a supplied clip registered once into an artifact a session can play in place of the avatar's source video (mint with scene.video_cache_id). The id is derived from the clip's content (md5 and size), not its URL, so the same bytes give the same id; a repeat request whose md5 and bytes are already built answers ready without a download. The answered id is bound to this workspace: only a scene the workspace prepared can be read back or minted, and a mint also requires it to be ready (409 scene_not_ready otherwise). 202 while building; poll GET /v1/scenes/{sceneId}. 200 once ready or failed. A failed state carries error: source_unreachable (the bytes never arrived; retry with a bounded backoff), source_unusable (supply a different clip), source_mismatch (the bytes differ from the declared md5 or bytes) or build_failed. Its scene_id is "unresolved" when the download failed before any byte was hashed and the request declared no md5 and bytes.

Requires an API key with the realtime:write scope.